The process for the preparation of a particulate olefin polymer catalyst component described in WO 00/08073 and 00/08074 includes a step in which a fraction of a magnesium dihalide-titanium tetrahalide-carboxylic acid ester complex is recovered by precipitation from solution. This precipitation is made by contacting the solution with a large amount of an aliphatic hydrocarbon. However, such precipitation leads to a tar-like reaction product of low catalytic activity, that needs to be washed several times in order to decrease the amount of inactive titanium complex. Such washing leads to a further decreased activity of the catalyst. Aromatic hydrocarbons have also been used for the precipitation, but they lead to a very finely divided precipitate which is difficult to deposit.
Moreover it is difficult to carry out such precipitations in a controlled and reproducible manner, leading to unsatisfactory product morphology, and to a variable and low concentration of butyl chloride in the product as a consequence of pre-precipitation evaporative removal of aliphatic solvent.